Explosives and other objectionable substances such as narcotics and polluting contaminants have long presented challenges regarding their early detection. In particular, explosives have been the subject of detection systems in recent times. Chemical detection of airborne traces of substances and imaging of apparatus which can potentially carry explosives have been developed and put into practice. However, these technologies have their limitations.
Explosives detection using THz and microwave radiation techniques is known, although this is in its infancy. Current devices tend to be large, underpowered, and have high input requirements. It is also known to provide explosives detectors which work at what has been called stand-off distances. However, devices which accomplish these functions have hereto for been large and not readily carried about. Such devices are suitable for stationary applications, such as security screening of persons entering protected facilities and premises, but are generally impractical for mobile applications wherein the apparatus is moved to different sites.